EP0762136A2 - Localisation de défauts de lignes - Google Patents

Localisation de défauts de lignes Download PDF

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Publication number
EP0762136A2
EP0762136A2 EP96306285A EP96306285A EP0762136A2 EP 0762136 A2 EP0762136 A2 EP 0762136A2 EP 96306285 A EP96306285 A EP 96306285A EP 96306285 A EP96306285 A EP 96306285A EP 0762136 A2 EP0762136 A2 EP 0762136A2
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EP
European Patent Office
Prior art keywords
point
carrier signal
cable
signal
induced signal
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP96306285A
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German (de)
English (en)
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EP0762136A3 (fr
Inventor
Robert G. Crick
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Individual
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Individual
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Publication date
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Publication of EP0762136A2 publication Critical patent/EP0762136A2/fr
Publication of EP0762136A3 publication Critical patent/EP0762136A3/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead

Definitions

  • the present invention relates generally to fault location in a paired line, and more particularly, to a device and method for locating faults in a paired line by monitoring a current induced in the paired line.
  • Paired Line encompasses coaxial cable, shielded cable and cable having more than two conductors wherein any two conductors of the cable may be a paired line.
  • a paired line is a conventional means of carrying telecommunications transmissions.
  • a paired line is typically two balanced conductors individually insulated and twisted together along their length in a spiral path.
  • a plurality of paired lines are usually bundled together to form a paired cable containing up to one hundred or more paired lines, wherein each paired line of the paired cable is capable of independently carrying a telecommunications signal.
  • a paired line is generally an effective telecommunications carrier, however, a fault can occasionally occur in a paired line limiting the effectiveness thereof. For example, a resistance fault can occur in a paired line when water invades the outer protective covering of a paired cable through an imperfection or other flaw therein.
  • the resulting resistance fault is a resistive contact between the two conductors of a paired line contained within the paired cable.
  • the resistance fault is also often accompanied by a resistance from one of the two conductors of the paired line to ground or to another conductor of the paired cable.
  • Another type of fault can occur when there is a discontinuity or break in the shield of a paired cable. The fault allows an increased coupling of extraneous voltages into one or more enclosed paired lines from sources, such as power transmission cables, near the paired cable.
  • Such faults typically cause noise in the affected paired line that is extremely disruptive to the clarity of the telecommunications signal sent over the paired line.
  • a fault in a paired line can also cause other problems such as circuit failure, arc-over and corrosion. Therefore, it is desirable to locate and repair faults in a paired line, particularly a paired line in a telecommunications cable.
  • Tone location methods are conventional noninvasive means for locating a short fault in a paired line of a telecommunications cable.
  • an audible tone is placed across the shorted conductors of the paired line by means of a tone transmitter and the tone is followed to the fault by a pickup coil placed on the paired line that is connected to an amplifier and a headset worn by an operator. Because no tone current flows past the short fault, the tone is audible up to the fault and inaudible beyond the fault, allowing the operator to precisely pinpoint the short fault to within a few centimeters of its actual location.
  • This tone location method is ineffective, however, for locating most resistance faults in a paired line.
  • One reason for such ineffectiveness is a phenomenon termed carry-by.
  • Carry-by occurs at faults that exceed a threshold resistance typically above about 2000 ohms. Most resistance faults have a resistance in a range between about 5000 to about 50,000 ohms.
  • the current of the audible tone produces a voltage across the conductors of the paired line past the fault. This voltage causes a corresponding tone current to flow into pair capacitance beyond the fault.
  • a tone will be audible beyond the resistance fault defeating the present tone location method.
  • the problem of carry-by is particularly acute when a high-frequency tone is present in the paired line, such as is typically employed in the present tone location method, because the magnitude of tone current flow past the fault is directly related to the frequency of the tone.
  • the tone transmitter drives less tone current through the paired line as the level of fault resistance increases.
  • the level of tone current available to the coil can drop below the background noise level present on a paired cable. Consequently, the background noise masks the location of the fault.
  • tone location method To overcome the limitations of the above-recited tone location method caused by carry-by, another tone location method has been developed in the telephone industry, wherein the conductors of the paired line are welded together at the fault using a 600-volt, breakdown test set. Welding of the conductors reduces fault resistance to zero in the paired line, thereby allowing effective tone location of the resistance fault.
  • This tone location method can cause extensive cable and equipment damage, particularly to plastic insulated cable and electronic central offices due to the high breakdown voltages used. Accordingly, this tone location method for overcoming fault resistance is disfavored.
  • An embodiment of the present invention provides a device and method for locating a fault in a paired line.
  • the device and method are particularly applicable to the location of a resistance fault in a paired line of a telecommunications cable.
  • the fault locating device comprises a base unit and a terminator unit each fixably connectable to an opposite end of the two conductors of a segment of a paired line believed to contain the fault.
  • the fault locating device further comprises a portable locator unit movable along the conductors of the paired line segment between the base unit and the terminator unit.
  • the locator unit has internal circuitry and an associated coil that is positioned proximal to the conductors of the paired line segment, such that the coil is in magnetic communication but not electrical communication with the paired line.
  • the internal circuitry of the locator unit includes a small, lightweight battery and a locator signal transmission circuit for creating a locator signal in the coil which couples a magnetic induced signal corresponding to the locator signal onto the conductors of the paired line segment.
  • the circuitry of the locator unit also includes a carrier signal processing circuit for receiving an encoded carrier signal traveling along the conductors from the base unit, decoding the carrier signal and communicating the decoded information to an operator in the form of an indicator, such as an audible tone or a visual display.
  • the base unit has circuitry including an induced signal receiver circuit for receiving the induced signal from the locator unit via the conductors of the paired line segment and a base carrier signal transmission circuit for creating and sending a base carrier signal having synchronization markers and values of a selected induced signal characteristic measured at the base unit and terminator unit encoded thereon.
  • the base unit also has a terminator carrier signal receiver circuit for receiving a terminator carrier signal having values of the selected induced signal characteristic measured at the terminator unit encoded thereon.
  • the base unit further includes noise nulling and synchronization circuitry for minimizing the effect of noise and carry-over received over the induced signal receiver circuit.
  • the terminator unit like the base unit, has an induced signal receiver circuit for receiving the induced signal from the locator unit via the conductors of the paired line segment.
  • the terminator unit also has a terminator carrier signal transmission circuit for creating and sending the terminator carrier signal.
  • the terminator unit has a base carrier signal receiver circuit for receiving the base carrier signal.
  • Operation of the fault locating device is performed by positioning the locator unit along the paired line segment near the base unit, wherein the fault is believed to be located between the locator unit and the terminator unit.
  • the locator unit is activated, creating the magnetic induced signal on the conductors of the paired line segment.
  • the magnetic induced signal travels along the conductors of the paired line segment and is received by the base unit and terminator unit.
  • the base unit In response to receipt of the induced signal, the base unit measures values of a selected induced signal characteristic at the base unit and encodes these values along with synchronization marks onto the base carrier signal. The base unit sends the resulting encoded base carrier signal to the locator unit.
  • the terminator unit similarly measures values of the selected induced signal characteristic at the terminator and encodes these values onto the terminator carrier signal. The terminator sends the encoded terminator carrier signal to the base unit which additionally encodes the values from the terminator carrier signal onto the base carrier signal.
  • the locator unit receives the base carrier signal, decodes the base carrier signal and continuously communicates the decoded values of the induced signal characteristic measured at the base unit and terminator unit to the operator by means of an indicator. The operator incrementally repositions the locator unit away from the base unit and toward the terminator unit along the path of the paired line segment as operation of the fault locating device proceeds.
  • the intensity or frequency of the indicator remains substantially constant except for some variation due to twisting of the conductors or changes in the relative position of the coil and the paired line (e.g., depth changes).
  • the intensity or frequency of the indicator abruptly drops, thereby establishing the precise location of the fault.
  • the voltage and frequency of the magnetic induced signal are narrowly specified in accordance with the present invention to satisfy the performance requirements of the fault locating device.
  • the voltage and frequency ranges of the induced signal are constrained at the upper end to satisfy the requirements that the induced signal on the paired line is inaudible to listeners and that the induced signal avoids excessive carry-by.
  • the voltage and frequency ranges of the induced signal are constrained at the lower end to satisfy the requirements that sufficient voltage is coupled onto the paired line by the coil of the locator unit to provide an induced signal exceeding background noise and that the resulting induced signal is detectable by both the base and terminator units.
  • the voltage and frequency of the induced signal are balanced between an upper and lower limit to achieve a fully-portable fault locating device having an inaudible, yet detectable, magnetic induced signal, that exceeds the background noise on the paired line while avoiding the effects of excessive carry-by. Achievement of these performance requirements is facilitated by noise nulling circuitry that reduces the noise on the paired line and synchronization circuitry that mitigates the impact of carry-by.
  • Figure 1 is a conceptual view of an illustrative fault locating device according to the present invention operably positioned in relation to a paired line.
  • Figure 2 is a block diagram of the locator unit shown in the device of Figure 1 configured to locate resistance faults in a paired line.
  • FIG. 3 is a block diagram of the base unit shown in the device of Figure 1.
  • Figure 4 is a block diagram of the terminator unit shown in the device of Figure 1.
  • Figures 5a, 5b, 5c depict conceptualized operation of a synchronous detector employed in the base unit of Figure 3.
  • Figure 6 is a block diagram of the locator unit shown in the device of Figure 1 configured to locate shield breaks in a shielded cable.
  • the fault locating device 10 has three basic components comprising a locator unit 12, a base unit 14, and a terminator unit 16.
  • the fault locating device 10 is operably positioned relative to a paired line 18, in which it is desired to locate a resistance fault 20, such that the base unit 14 engages a first conductor 22 and a second conductor 24 of the paired line 18 at a base point 26 on the paired line 18 and the terminator unit 16 engages the first and second conductors 22, 24 at a terminator point 28 on the paired line 18.
  • the base point 26 and the terminator point 28 are positioned at opposite ends of a segment 30 of the paired line 18 that is selected to encompass the fault 20, at least to the best approximation of the operator. If it is subsequently determined that the selected paired line segment does not encompass the fault, the paired line segment is simply reselected until a paired line segment is selected encompassing the fault in accordance with a method described hereafter. In any case, for purposes of illustration, the paired line segment 30 of Figure 1 is shown to encompass the fault 20.
  • the illustrative fault locating device 10 has general utility to paired lines employed in a number of paired cable applications, including power transmission and communications paired cable applications.
  • the fault locating device 10 has particular utility to paired lines employed in telecommunications paired cable applications, including accessible paired cables, such as aerial paired cables, and inaccessible paired cables, such as buried paired cables.
  • a paired line is substantially any line having at least two continuous electrical conductors that, in the absence of a fault, are electrically insulated from one another.
  • the two conductors can each be solid or braided wires, grounded or ungrounded and having parallel or spiral paths.
  • one conductor can be a wire and the other conductor can be a conductive tubular shield enclosing the wire.
  • the above-recited definition of a paired line encompasses coaxial cable, shielded cable, and cable having more than two conductors, wherein any two conductors of the cable may be deemed to define a paired line for purposes of the invention.
  • a paired line as defined herein includes a shielded cable having a shield and a conductor enclosed within the shield.
  • a fault is defined herein as any unintended perturbation in the path of a conductor that undesirably draws current therefrom, such as a short, a cross, a ground, or a split.
  • the fault 20 disclosed herein is characterized as a resistance fault, it being understood that the device 10 is applicable to the location of many types of faults as generally defined above.
  • the locator unit 12 is operably positioned proximal to a locator point 32 on the paired line 18 that is between the base point 26 and terminator point 28. As such, the locator unit 12 preferably does not electrically engage the conductors 22, 24, but is sufficiently proximal to the conductors 22, 24 to produce an induced signal therein as will be described hereafter.
  • the base and terminator points 26, 28 are preferably selected at points on the paired line 18 where relatively convenient electrical access to the conductors 22, 24 is provided, such as a junction box or other splice location.
  • Base pickup lines 34, 36 extend from the base unit 14 and having electrically conductive pickups such as conventional alligator clips or the like on the ends of the lines 34, 36 that are removably connected to the conductors 22, 24.
  • a base ground line 38 is also provided connecting the base unit 14 to a ground 40.
  • terminator pickup lines 42, 44 extend from the terminator unit 16 and removably connected to the conductors 22, 24.
  • a terminator ground line 46 is provided connecting the terminator unit 16 to a ground 48.
  • the position of the base point 26, and correspondingly the position of the base unit 14, are substantially fixed with respect to the paired line 18 during a given fault locating sequence.
  • the position of the terminator point 28, and correspondingly the position of the terminator unit 16, are likewise substantially fixed with respect to the paired line 18 during a given fault locating sequence.
  • the position of the locator point 32 is variable along the length of the paired line 18 throughout a given fault locating sequence as a function of the fixed position of the fault 20 on the paired line 18. Accordingly, the locator unit 12 has a fully mobile, unanchored, portable configuration, the locator unit 12 being relatively compact and lightweight to render it manually transportable by a single operator.
  • the locator unit 12 is shown to comprise a unitary housing 50 and a probe 52 positioned outside the housing 50.
  • a connective member 53 extends between the probe 52 and the housing 50.
  • the housing 50 is preferably a hardened protective shell and the connective member 53 is preferably a flexible or rigid tube.
  • the probe 52 can alternatively be positioned within the housing 50, thereby eliminating the connective member 53.
  • the specific components of the locator unit 12 are described with further reference to the block diagram of Figure 2.
  • the probe 52 is shown schematically to enclose a coil 54 electrically connected by coil lines 56a, 56b to the circuitry of the locator unit 12.
  • the coil 54 can have a number of configurations depending on the specific application of the fault locating device 10. For locating faults in an inaccessible paired line, a relatively large remote coil is provided, typically having an elongated magnetic core or other geometry sufficient to meet the performance requirements of the locator unit 12. For locating faults in an accessible paired line, a relatively small contact coil is provided.
  • the circuitry of the locator unit 12 comprises a locator signal transmission circuit 58 and a carrier signal processing circuit 60.
  • the locator signal transmission circuit 58 provides a pathway from a microcontroller 62 to the coil 54 for a locator signal capable of producing a magnetic induced signal in the paired line 18. Included in series within the locator signal transmission circuit 58 in a direction away from the microcontroller 62 toward the coil line 56a are a synchronized oscillator 64, a locator signal power driver 66, and a carrier signal rejection filter 68.
  • the locator signal transmission circuit 58 and the carrier signal processing circuit 60 are in electrical communication with the coil 54 via the coil line 56a.
  • the carrier signal processing circuit 60 provides a pathway for a carrier signal from the coil 54 to the microcontroller 62. Included in series within the carrier signal processing circuit 60 in the direction away from the coil line 56a toward the microcontroller 62 are a locator signal rejection filter 72, a carrier signal preamplifier 74, a switch 76 and a carrier signal receiver 78.
  • the carrier signal processing circuit 60 splits into two parallel pathways after the carrier signal receiver 78 with a first parallel pathway 80 including a limiter 82 and a decoder 84 and a second parallel pathway 86 including a magnitude detector 88.
  • the term "limiter" is defined to encompass a conventional limiter or, in the alternative, an automatic gain control.
  • the first and second parallel pathways 80, 86 feed into the microcontroller 62 through an analog to digital converter 90.
  • the locator unit 12 is further provided with a visual display 92 and an audio speaker 94 in parallel electrical communication with the microcontroller 62, enabling the locator unit 12 to communicate an indicator both visually and audibly to an operator of the device 10.
  • the microcontroller 62 disclosed herein is a digital microprocessor. It is nevertheless apparent to the skilled artisan that within the scope of the present invention an analog controller can be substituted for the digital microprocessor within the circuits 58, 60 without substantially altering the capabilities of the present fault locating device 10.
  • the analog to digital converter 90 is omitted from the carrier signal processing circuit 60 in the case where an analog controller is substituted for a digital microprocessor as the microcontroller 62.
  • a DC power source 96 is additionally included in the housing 50 of the locator unit 12. The power source 96 supplies power to the components of the locator unit 12 enabling the functions thereof.
  • the power source 96 is preferably a relatively small, lightweight battery pack, such as one or more dry-cell or rechargeable batteries (e.g., 9-volt or D-cell batteries).
  • microcontroller 62 synchronized oscillator 64 and decoder 84 are shown and described herein as discrete structural components having related functions. In practice, these discrete components can be integrated into a single digital microprocessor structure performing the same functions ascribed to the discrete components in a manner apparent to the skilled artisan.
  • the switch 76 of locator unit 12 has two functional positions providing alternate capabilities therefor.
  • the coil 54 and carrier signal processing circuit 60 function as a magnetic carrier signal pickup, primarily for receiving magnetic carrier signals from the base unit 14 as described hereafter.
  • a capacitive ground reference circuit 98 is enabled which, in cooperation with the coil 54, functions as a capacitive pickup primarily for locating cable shield breaks as described hereafter.
  • the capacitive ground reference circuit 98 includes a capacitive ground reference 100 and a capacitive signal preamplifier 102 on one side of the switch 76.
  • the remainder of the capacitive ground reference circuit 98 on the opposite side of the switch 76 is identical to the carrier signal processing circuit 60, including the carrier signal receiver 78, first and second parallel pathways 80, 86, analog to digital converter 90 and microprocessor 62.
  • the capacitive ground reference 100 is simply the housing 50. If the housing 50 is not electrically conductive, however, the capacitive ground reference 100 can be provided by a metallic shield (not shown) contained within the housing 50. In either case, the capacitive ground reference 100 couples to the body of an operator, which provides adequate ground reference for a carrier signal when the operator is standing on the earth. Although not shown, the capacitive ground reference 100 can alternatively be a grounding lead and grounding connection connected to a cable shield.
  • the circuitry of the locator unit 12 further comprises a locator circuit common 104.
  • the locator circuit common 104 is electrically connected to the locator signal power driver 66, carrier signal preamplifier 74 and capacitive carrier preamplifier 102.
  • the specific components of the base unit 14 are described with further reference to the block diagram of Figure 3. Substantially all of the circuitry of the base unit 14 is enclosed in a housing 200 comprising a hardened protective shell.
  • the circuitry of the base unit 14 includes an induced signal receiver circuit 202 and a base unit carrier signal transmission circuit 204. As described above, the base pickup lines 34, 36 extend from the base unit 14 and removably connect with the conductors 22, 24 to provide electrical communication between the circuits 202, 204 and the paired line 18.
  • the induced signal receiver circuit 202 is configured to receive the induced signal originating at the locator point 32 and sent therefrom along the paired line 18.
  • a variable gain amplifier 206 included in series within the induced signal receiver circuit 202 in a direction away from the paired line 18 are a variable gain amplifier 206, a bandpass filter 208, a synchronous detector 210, a lowpass filter 212, an analog to digital converter 214 and a microcontroller 216.
  • a low impedance input termination 218 positioned between the base pickup lines 34, 36 and the variable gain amplifier 206.
  • the low impedance input termination 218 comprises a first inlet pathway 220 and a second inlet pathway 222.
  • the first inlet pathway 220 is connected to a base circuit common 224 through a first balanced resistor 226 and a first balanced capacitor 228 in parallel.
  • the second inlet pathway 222 is connected to the base circuit common 224 through a second balanced resistor 230 and a second balanced capacitor 232 in parallel.
  • the first and second balanced resistors 226, 230 are substantially equal in resistance to provide, in series, an input terminating resistance across the base pickup lines 34, 36. As such, the first and second balanced resistors 226, 230 provide a balanced center tap of the low impedance input termination 218 connected to the base circuit common 224.
  • the first and second balanced capacitors 228, 232 are also substantially equal in value to provide a relatively low impedance path from the base pickup lines 34, 36 to the base circuit common 224 for the higher frequency carrier signals while providing a balanced relatively high impedance to the lower frequency induced signal.
  • the first and second inlet pathways 220, 222 feed into a differential signal preamplifier 234 that is connected in series to a summing amplifier 236 and the variable gain amplifier 206.
  • a line balancing pathway 238 is provided having a balancing switch 240 that enables selective connection of the first or second inlet pathway 220 or 222 to the base grounding line 38 through a line balancing variable impedance 242.
  • the base ground line 38 is connected to the ground 40 by a ground pickup 244.
  • a switching line 246 extends from the base ground line 38 having a resistor 248 and a grounding switch 250 in series. When closed, the grounding switch 250 connects the base circuit common 224 to the ground 40 through the resistor 248.
  • a noise nulling circuit 252 feeds into the low impedance input termination 218 from the base ground line 38.
  • the noise nulling circuit 252 includes in series a variable gain amplifier 254, a variable phase shifter 256, and a three-way switch 258.
  • a first position of the switch 258 connects the noise nulling circuit 252 with the first inlet pathway 220 through a first summing impedance 260
  • a second position of the switch 258 connects the noise nulling circuit 252 with the second inlet pathway 222 through a second summing impedance 262
  • a third position of the switch 258 connects the noise nulling circuit 252 with the summing amplifier 236 through a summing input line 263.
  • the base carrier signal transmission circuit 204 is configured to send an encoded carrier signal from the base unit 14 along the paired line 18 to the locator unit 12 and the terminator unit 16. Included in series within the base carrier signal transmission circuit 204 in the direction of the paired line 18 are the microcontroller 216, an encoder 264, and a carrier signal driver 266.
  • a carrier signal oscillator 268 electrically communicates with the encoder 264 and a locator synchronization oscillator 269 is provided in electrical communication with the microcontroller 216 and the synchronous detector 210.
  • the carrier signal driver 266 is referenced to the base circuit common 224 and connected to the base grounding line 38 through a capacitor 270.
  • the base unit 14 is also provided with a terminator carrier signal receiver circuit 272 configured to receive an encoded carrier signal originating at the terminator unit 16 and sent to the base unit 14 along the paired line 18.
  • the carrier signal receiver circuit 272 is connected to the base ground line 38 through a capacitor 274. Included in series within the terminator carrier signal receiver circuit 272 in a direction away from the capacitor 274 are a carrier signal receiver 276, a limiter 278, a decoder 280, and the microcontroller 216.
  • the microcontroller 216 disclosed herein is a digital microprocessor.
  • an analog controller can be substituted for the digital microprocessor within the circuits 202, 204, 272 without substantially altering the capabilities of the present fault locating device 10.
  • the analog to digital converter 214 is omitted from the induced signal receiver circuit 202 in the case where an analog controller is substituted for a digital microprocessor as the microcontroller 216.
  • a DC power source 282 is additionally included in the housing 200 of the base unit 14. The power source 282 supplies power to the components of the base unit 14 enabling the functions thereof.
  • the power source 282 is preferably one or more relatively small, lightweight batteries.
  • microcontroller 216 encoder 264, decoder 280 and oscillators 268, 269 are shown and described herein as discrete structural components having related functions. In practice, these discrete components can be integrated into a single digital microprocessor structure performing the same functions ascribed to the discrete components in a manner apparent to the skilled artisan.
  • the specific components of the terminator unit 16 are described with further reference to the block diagram of Figure 4. Substantially all of the circuitry of the terminator unit 16 is enclosed in a housing 400 comprising a hardened protective shell.
  • the circuitry of the terminator unit 16 includes an induced signal receiver circuit 402 and a terminator carrier signal transmission circuit 404. As described above, the terminator pickup lines 42, 44 extend from the terminator unit 16 and connect with the conductors 22, 24 to provide electrical communication between the circuits 402, 404 and the paired line 18.
  • the induced signal receiver circuit 402 is configured to receive the induced signal originating at the locator point 32 and sent therefrom along the paired line 18.
  • the induced signal receiver circuit 402 of the terminator unit 16 is substantially similar to the induced signal receiver circuit 202 of the base unit 14 shown in Figure 3. Included within the induced signal receiver circuit 402 in a direction away from the paired line 18 are a variable gain amplifier 406, a bandpass filter 408, a synchronous detector 410, a lowpass filter 412, an analog to digital converter 414 and a microcontroller 416. Further included within the induced signal receiver circuit 402 is a high impedance input termination 418 positioned between the terminator pickup lines 42, 44 and the variable gain amplifier 406. The high impedance input termination 418 is specified to provide a relatively high impedance to the induced signal voltage so that the terminator unit 16 does not draw induced signal current past the fault as is described hereafter.
  • the high impedance input termination 418 comprises a first inlet pathway 420 and a second inlet pathway 422.
  • the first inlet pathway 420 is connected to a terminator circuit common 424 through a first balanced resistor 426 and a first balanced capacitor 428 in parallel.
  • the second inlet pathway 422 is connected to the terminator circuit common 424 through a second balanced resistor 430 and a second balanced capacitor 432 in parallel.
  • the first and second balanced resistors 426, 430 are substantially equal in resistance, having a relatively high value on the order of about 1 megohm to provide in series an input terminating resistance across the terminator pickup lines 42, 44.
  • the first and second balanced resistors 426, 430 provide a balanced center tap of the high impedance input termination 418 connected to the terminator circuit common 424.
  • the first and second balanced capacitors 428, 432 are also substantially equal in value to provide a relatively low impedance path from the terminator pickup lines 42, 44 to the terminator circuit common 424 for the higher frequency carrier signals while providing a balanced relatively high impedance to the lower frequency induced signal.
  • the first and second inlet pathways 420, 422 feed into a differential signal preamplifier 434 that is connected in series to the variable gain amplifier 406.
  • the terminator carrier signal transmission circuit 404 is configured to send an encoded carrier signal from the terminator unit 16 along the paired line 18 to the base unit 14. Accordingly, the carrier signal transmission circuit 404 of the terminator unit 16 is substantially similar to the carrier signal transmission circuit 204 of the base unit 14 shown in Figure 3. Included in series within the terminator carrier signal transmission circuit 404 in the direction of the paired line 18 are the microcontroller 416, an encoder 436, and a carrier signal driver 438. A carrier signal oscillator 440 communicates with the encoder 436. The carrier signal driver 438 is connected to the terminator ground line 46 through a capacitor 442 and a terminator ground pickup 444. A terminator synchronization oscillator 446 is provided in electrical communication with the microcontroller 416 and the synchronous detector 410.
  • the terminator unit 16 is also provided with a base carrier signal receiver circuit 448 configured to receive an encoded carrier signal originating at the base unit 14 and sent to the terminator unit 16 along the paired line 18.
  • the carrier signal receiver circuit 448 is connected to the terminator ground line 46 through a capacitor 450. Included in series within the base carrier signal receiver circuit 448 in a direction away from the capacitor 450 are a carrier signal receiver 452, a limiter 454, a decoder 456, and the microcontroller 216.
  • the microcontroller 416 disclosed herein is a digital microprocessor. It is nevertheless apparent to the skilled artisan that within the scope of the present invention an analog controller can be substituted for the digital microprocessor within the circuits 402, 404 without substantially altering the capabilities of the present fault locating device 10.
  • the analog to digital converter 414 is omitted from the induced signal receiver circuit 402 in the case where an analog controller is substituted for a digital microprocessor as the microcontroller 416.
  • a DC power source 458 is additionally included in the housing 400 of the terminator unit 16. The power source 458 supplies power to the components of the terminator unit 16 enabling the functions thereof.
  • the power source 458 is preferably one or more relatively small, lightweight batteries.
  • microcontroller 416, encoder 436, decoder 456 and oscillators 440, 446 are shown and described herein as discrete structural components having related functions. In practice, these discrete components can be integrated into a single digital microprocessor structure performing the same functions ascribed to the discrete components in a manner apparent to the skilled artisan.
  • a segment 30 of a paired line 18 is identified that is believed to contain a fault 20.
  • the paired line segment 30 is typically up to about 5000 meters in length and can comprise the entire length of the paired line 18, if the paired line is 5000 meters or less in length.
  • the base unit 14 is fixably positioned at a base point 26 that is at one end of the paired line segment 30 and the terminator unit 16 is fixably positioned at a terminator point 28 that is at the other end of the paired line segment 30.
  • the base pickup lines 34, 36 are removably connected to the first and second conductors 22, 24 at the base point 26 and the terminator pickup lines 42, 44 are similarly removably connected to the first and second conductors 22, 24 at the terminator point 28.
  • the method of locating the fault 20 is initiated by positioning the probe 52 of the locator unit 12 proximal to a selected locator point 32 on the paired line 18 between the base point 26 and terminator point 28.
  • the actual position of the locator point 32 is variable, rather than fixed, during operation of the fault locating device 10.
  • the locator point 32 is preferably positioned near the base point 28 during initial operation of the device 10 such that the fault 20 is located somewhere along the paired line segment 30 between the locator point 32 and the terminator point 28.
  • the locator point 32 is then incrementally repositioned toward the terminator point 28 as operation of the device 10 proceeds.
  • the relative distance between the probe 52 and conductors 22, 24 at any given locator point 32 is termed the induction distance.
  • the maximum allowable induction distance is a function of the power output of the locator unit 12, the size and configuration of the coil 54, and the desired voltage of the signal induced in the conductors 22, 24.
  • a typical maximum allowable induction distance is up to about 1 meter using a relatively large remote induction coil 54 for inaccessible buried paired cable and up to about 0.06 meters using a relatively smaller contact induction coil 54 for accessible paired cable.
  • the microprocessor 62 directs the synchronized oscillator 64 and locator signal power driver 66 to generate a synchronized AC locator signal utilizing the DC power source 96.
  • the resulting locator signal is sent to the coil 54 via the locator signal transmission circuit 58 where the coil 54 magnetically couples the locator signal into the paired line 18 to produce a magnetic induced signal in the paired line 18 at the locator point 32.
  • the voltage and frequency of the induced signal are selected within ranges that satisfy the performance requirements of the fault locating device 10. In particular, the voltage and frequency ranges of the induced signal are limited at the upper end by the requirement that the induced signal on the paired line 18 be inaudible to listeners and by the requirement that the induced signal on the paired line 18 avoid excessive carry-by.
  • a signal having both a very low voltage and a very low frequency satisfies the requirements of being inaudible and avoiding significant carry-by.
  • Such a signal may fail to satisfy other performance requirements of the device 10, lacking sufficient voltage to exceed the background noise and lacking sufficient frequency to be coupled onto the paired line 18 by the coil 54. If the frequency of the induced signal is raised to improve the detectability thereof, the induced signal may become overly susceptible to carry-by. Alternatively, if the voltage of the induced signal is raised to overcome the background noise, excessive battery power may become necessary, defeating the portability of the detector unit 12.
  • the frequency of the induced signal is typically selected in a range less than about 300 Hz, preferably in a range between about 200 Hz and about 1 Hz, and most preferably at a value of about 35 Hz.
  • the corresponding voltage of the induced signal is typically selected in a range between about 0.1 microvolt and 100 microvolts and preferably at a value of about 1 microvolt, which is generally greater than ambient noise after noise nulling.
  • the induced signal satisfying the above-recited criteria travels along the conductors 22, 24 to the base unit 14 and the terminator unit 16.
  • the base pickup lines 34, 36 receive the induced signal and carry the induced signal to the induced signal receiver circuit 202 having the noise nulling circuitry incorporated therein.
  • the differential signal preamplifier 234 amplifies the induced signal received by the low impedance input termination 218 from the base pickup lines 34, 36.
  • the differential signal preamplifier 234 is also equipped with a DC blocking mechanism to remove DC biases present on the paired line 18.
  • the summing amplifier 236 adds the output of the differential signal preamplifier 234 to the output of the noise nulling circuit 252 enabling the operator to reduce the effects of noise on the conductors 22, 24 received by the base unit 14.
  • noise nulling enables the operator to cancel the unbalanced voltage on the paired line 18 by summing a portion of the common mode voltage present between the conductors 22, 24 and the ground 40 at the base point 26 with the differential voltage present across the paired line 18, in proper phase and magnitude. Summing of these voltages causes substantial cancellation of the noise induced onto the paired line 18 by the unbalance often present at the fault 20.
  • the noise nulling circuitry effectuates noise nulling by means of the low impedance input termination 218.
  • the first and second balanced resistors 226, 230 of the low impedance input termination 218 are connected to the base circuit common 224 having a high impedance to earth ground, thereby functioning to reject common mode signals to ground while referencing the base circuit common 224 to the common mode (longitudinal) voltage present on the conductors 22, 24.
  • the low impedance input termination 218 is augmented by selecting one or more of the noise nulling techniques described hereafter that are enabled by the circuitry of the base unit 14.
  • summing amplifier nulling In accordance with a technique termed summing amplifier nulling, the common mode voltage of the induced signal between the conductors 22, 24 and the ground 40 is processed by the variable gain amplifier 254 and the variable phase shifter 256 and summed into the summing amplifier 236. The gain and phase of the induced signal are adjusted to null the imbalance voltage beyond the summing amplifier 236.
  • An alternate technique termed summing impedance nulling likewise processes the common mode voltage with the variable gain amplifier 254 and the variable phase shifter 256.
  • the resulting signal is applied to one side of the low impedance input termination 218 through the summing impedance 260, 262 or a resistor (not shown) substituted therefor, while the switch 258 disconnects the summing input line 263 causing the summing amplifier 236 to function as a buffer amplifier for signals from the differential signal preamplifier 234.
  • Proper adjustment of the gain and phase balances out the noise at the input to the differential signal preamplifier 234 and simultaneously reduces the noise level on the conductors 22, 24.
  • a technique termed line balancing with grounded termination center tap also has utility in conjunction with either of the previously recited techniques.
  • the grounding switch 250 is closed, effectively grounding the center tap of the low impedance input termination 218.
  • the switch 240 is closed to the side of the inlet pathway 220 or 222 producing the greatest noise cancellation.
  • the line balancing variable impedance 242 is then adjusted, if required, to minimize noise.
  • the output of the summing amplifier 236 passes to the variable gain amplifier 206 where the voltage of the induced signal is further amplified and, if desired, adjusted for differences in the signal due to fault resistance losses.
  • the bandpass filter 208 which is tuned to the relatively low frequency of the induced signal, rejects extraneous signals from the output of the variable gain amplifier 206 that have surrounding frequencies. In particular, the bandpass filter 208 attenuates interference from 50/60 Hz signals that are magnetically induced onto the paired line 18 by adjacent power lines.
  • the synchronous detector 210 is driven by the locator synchronization oscillator 269 which is synchronized with generation of the locator signal at the locator unit 12, thereby synchronizing operation of the base unit 14 and locator unit 12.
  • Synchronous operation of the base unit 14 and locator unit 12 in conjunction with the use of an induced signal having a relatively low frequency enables the effective location of faults having resistances above 50 kohms without a significant impact from carry-by, even in relatively long paired line segments 30 having lengths up to 5000 meters.
  • Low frequency operation tends to decrease carry-by because lowering the frequency of the induced signal increases the capacitive reactance of the paired line 18, reducing the magnitude of induced signal current flow past the fault 20.
  • the synchronous detector 210 supplements this effect by detecting only the current of the induced signal flowing through the fault resistance and rejecting any carry-by occurring due to current flow into capacitance that leads resistive current by 90°.
  • the low frequency induced signal has the added advantage of exhibiting substantially less attenuation over length of the paired line segment 30 than would a higher frequency induced signal.
  • Synchronous detection further enables the operator to observe changes in polarity due to twisting of the conductors 22, 24. This permits the operator to differentiate between carry-by and the induced signal in the presence of unbalanced conductor faults and ground faults both of which are more susceptible to carry-by than balanced conductor faults.
  • the principle by which the synchronous detector 210 operates is described with reference to Figure 5a, 5b and 5c. Operation of the synchronous detector 210 in association with the fault locating device 10 of Figure 1 is the functional equivalent of a circuit 600 shown in Figure 5a.
  • the circuit 600 has a switch 602 that is opened and closed in synchronism with the induced signal at the locator unit 14.
  • the circuit 600 further includes a series resistor 604 and, in parallel, a resistor 606, a capacitor 608 and an amplifier 610 such that the output voltage of the circuit 600 is the average input voltage of the circuit 600 when the switch 602 is closed.
  • the switch 602 is opened and closed as shown in Figure 5b by the switch waveform 612.
  • Figure 5c shows the input voltage waveform of the circuit 600 as the sum of two distinct waveforms, a resistance current waveform 614 and a capacitance current waveform 616.
  • the capacitance current waveform 616 of the carry-by leads the resistance current waveform 614 by 90°, thereby averaging to zero as indicated by the shaded area under the capacitance current waveform 616 of Figure 5c.
  • the entire fault resistance current waveform 614 is in phase with the induced signal and the switch waveform 612, thereby enabling detection of the resistance fault.
  • the lowpass filter 212 filters the rectified DC signal from the synchronous detector 210, allowing a narrowing of the circuit bandwidth to more effectively filter out 50/60Hz signals and other extraneous signals having undesired frequencies.
  • the analog to digital converter 214 converts the analog voltage values of the DC signal produced by the lowpass filter 212 to digital values for processing by the microcontroller 216 which is shown herein to be a digital microprocessor. It also is within the purview of the skilled artisan to substitute an analog controller for a digital microprocessor as the microcontroller 216, in which case the analog to digital converter 214 is omitted from the base unit 14.
  • the microcontroller 216 configures the circuitry of the base unit 14 for its various modes of operation, including receiving and reading the induced signal and encoding and sending a carrier signal.
  • the microcontroller 216 specifies values of an induced signal characteristic that are encoded onto a carrier signal created by the base unit 14 and sent to the locator unit 12.
  • the induced signal is disclosed herein as being characterized in terms of the magnitude of its voltage.
  • the induced signal can alternatively be specified in terms of characteristics other than voltage magnitude, such as phase shifts.
  • the carrier signal transmission circuit 204 of the base unit 14 creates a carrier signal having values of the selected characteristic for the induced signal and having synchronization marks encoded therein.
  • the synchronization marks enable the locator unit 12 to create the induced signal in synchronization with operation of the synchronous detector 210 at the base unit 14 so that carry-by is reduced.
  • the encoded base carrier signal is created by delivering values of the voltage magnitude of the induced signal measured at the base unit 12 from the microcontroller 216 to the encoder 264.
  • the synchronization marks are similarly delivered from the microcontroller 216 to the encoder 264.
  • the encoder 264 imprints this information onto the base carrier signal in the form of a digital or analog code.
  • the encoded base carrier signal is sent in synchronization with the locator unit 12 by means of the carrier signal oscillator 268 and carrier signal driver 266 to the locator unit 12.
  • the carrier signal driver 266 drives the carrier signal current out through the capacitor 270 and ground pickup 244 to the ground 40, forcing an opposing current flow from the carrier signal driver 266, into the base circuit common 224, through the first and second balanced capacitors 228, 232, into the base pickup lines 34, 36, and onto the paired line 18.
  • the capacitor 270 provides a low impedance path to the ground 40 for the carrier signal while providing a high impedance for the induced signal from the locator unit 12.
  • the encoded base carrier signal has a frequency range greater than about 5 kHz, preferably a frequency range between about 5 kHz and about 100 kHz, and most preferably a frequency value of about 10 kHz.
  • the encoded base carrier signal typically has a voltage below about 150 volts within the prescribed frequency range and preferably has a voltage of about 25 volts.
  • the base carrier signal When the encoded base carrier signal reaches the locator unit 12 via the conductors 22, 24, the base carrier signal is received magnetically by the coil 54 within the probe 52 positioned at the locator point 32.
  • the base carrier signal is sent along the coil line 56a to the carrier signal receiver circuit 60 while entry to the locator signal transmission circuit 58 is blocked by means of the carrier signal rejection filter 68.
  • the carrier signal passes through the locator signal rejection filter 72, which blocks entry of the locator signal into the carrier signal processing circuit 60, and is fed to the carrier signal preamplifier 74.
  • the carrier signal is amplified in the carrier signal preamplifier 74 and delivered to the carrier signal receiver 78 through the closed switch 76.
  • the carrier signal receiver 78 feeds the amplified signal to the limiter 82 where the amplitude of the signal is limited thereby and then to the decoder 84 where the encoded information on the carrier signal is read.
  • the decoded information which comprises the synchronization marks and values of the selected characteristic specifying the induced signal (in this case voltage magnitude measured at the base unit 14), is transmitted from the decoder 84 to the microcontroller 62 for processing after the decoded information is passed through the analog to digital converter 90 for digital conversion.
  • the magnitude detector 88 simultaneously evaluates the amplified signal from the carrier signal receiver 78 to determine the magnitude of the carrier signal for processing by the microcontroller 62, whether the signal has originated from the magnetic carrier receiver circuit 58 or the capacitive ground reference circuit 102, as will be described hereafter.
  • the magnitude detector 88 sends values of the magnitude of the carrier signal to the microcontroller 62 after it has passed through the analog to digital converter 90 for digital conversion.
  • an analog controller for a digital microprocessor as the microcontroller 62, in which case the analog to digital converter 90 is omitted from the locator unit 12.
  • the microcontroller 62 directs operation of the synchronized oscillator 64, display 92, speaker 94 in correspondence with the decoded information received from the decoder 84.
  • the synchronization marks are translated into instructions that are sent to the synchronized oscillator 64 for synchronized operation thereof.
  • Values of the voltage magnitude for the induced signal are similarly translated into instructions that are sent to the speaker 94 for generating a audible correlation of the voltage magnitude in the form of a continuous audible tone having an intensity or frequency directly related to the values of the voltage magnitude for the induced signal received by the base unit 14.
  • the intensity or frequency of the tone generated by the speaker 94 increases.
  • the intensity or frequency of the tone generated by the speaker 94 decreases.
  • the presence of the fault 20 causes a drop in the magnitude of the voltage for the induced signal, because the voltage of the induced signal divides between the resistance of the fault 20 and the low resistance of the low impedance input termination 218 of the base unit 14.
  • the fault resistance draws current, current also flows through the low impedance input termination 218 producing a voltage drop detectable by the base unit 14. If the locator unit approaches the fault 20 from the base point 26, the base unit 14 will detect voltage due to current flow in the fault resistance.
  • This voltage may rise and fall and reverse in polarity as the coil 54 is moved along the paired cable containing the paired line segment 30 due to the twist of the conductors 22, 24 and the spiraling of the paired line segment 30 within the paired cable, but will remain continuous before the fault 20 is reached.
  • Polarity changes can be communicated to the operator by a change in a characteristic of the audible tone in correspondence with polarity changes. In any case, when the locator unit 12 passes the fault 20, the base unit 14 no longer detects any voltage, while the terminator unit 16 detects full voltage as described hereafter.
  • the fault 20 in the segment 30 of the paired line 18 is located by shifting the locator unit 12 along the segment 30 away from the base point 26 in the direction of the terminator point 28 to establish incrementally new locator points 32 therebetween.
  • the fault 20 is precisely located at the point on the segment 30 where the intensity or frequency of the tone from the speaker 94 is strong followed by an abrupt drop in the intensity or frequency of the tone as the locator unit 12 continues in the direction of the terminator point 28.
  • the display 92 provides a quantitative visual verification of the information communicated to the operator by the speaker 94.
  • the display 92 is a visual correlation of the voltage magnitude in the form of either an analog or a digital readout of the values of the voltage magnitude for the induced signal as the locator unit 12 is conveyed along the paired line 18.
  • the terminator unit 16 supplements the present method of fault location by providing an auxiliary encoded carrier signal responsive to the induced signal of the locator unit 12.
  • the encoded carrier signal of the terminator unit 16 confirms location of the fault 20 when read in conjunction with the encoded carrier signal of the base unit 14.
  • the induced signal originating at the locator point 32 travels to the terminator point 28 where it is received by the terminator unit 16 and processed in a manner similar to that of the base unit 14.
  • the induced signal is delivered from the conductors 22, 24 to a high impedance input termination 418 by the terminator pickup lines 42, 44 that are removably connected to the conductors 22, 24.
  • the high impedance input termination 418 is balanced in substantially the same manner as the low impedance input termination 218 of the base unit 14, but lacks the associated noise nulling circuitry of the base unit 14 because the termination unit 16 receives a stronger signal than the base unit 14 that is not attenuated by fault resistance.
  • the termination unit 16 also has a high input impedance preventing it from drawing the induced signal when the locator unit 12 is between the fault 20 and the terminator unit 16.
  • the differential signal preamplifier 434 receives the induced signal from the high impedance input termination 418 and amplifies the induced signal.
  • the output of the differential signal preamplifier 418 passes to the variable gain amplifier 406 where the voltage of the induced signal is further amplified and, if desired, adjusted for differences in the signal due to coil coupling losses.
  • the bandpass filter 408 attenuates interference from 50/60 Hz signals that are magnetically induced onto the paired line 18 by adjacent power lines.
  • the synchronous detector 410 in conjunction with the locator synchronization oscillator 264 functions to detect the induced signal in synchronism with the locator signal generated by the locator unit 12 and induced into the paired line 18 by the coil 54. It is noted, however, that since capacitance does not cause a substantial capacitive component in the voltage received by the terminator unit 16, a standard detector may alternatively be substituted for the synchronous detector 410 of the terminator unit 16 without significant loss of performance.
  • synchronous operation of the terminator unit 16 is substantially similar to that described above with respect to the base unit 14 such that the terminator unit 16 detects the induced signal in synchronization with generation of the signal at the locator unit 12 and sends the terminator carrier signal in synchronization with receipt of the carrier signal from the base unit 14.
  • the lowpass filter 412 filters the rectified DC signal from the synchronous detector 410, allowing a narrowing of the circuit bandwidth to more effectively filter out 50/60Hz signals and other extraneous signals having undesired frequencies.
  • the analog to digital converter 414 converts the analog voltage values of the DC signal produced by the lowpass filter 412 to digital values for processing by the microcontroller 416 which is shown herein to be a digital microprocessor. It is also within the purview of the skilled artisan to substitute an analog controller for a digital microprocessor as the microcontroller 416, in which case the analog to digital converter 414 is omitted from the terminator unit 16. In either case, the microcontroller 416 configures the circuitry of the terminator unit 16 for its various modes of operation, including receiving and reading the induced signal and encoding and sending a carrier signal.
  • the carrier signal transmission circuit 404 of the terminator unit 16 creates a terminator carrier signal having values of the voltage magnitude for the induced signal encoded thereon.
  • an alternate characteristic specifying the induced signal can be selected, such as phase shift.
  • the terminator carrier signal is created by delivering values of the selected characteristic for the induced signal (i.e., values of the voltage magnitude in this case) measured at the terminator unit 16 from the microcontroller 416 to the encoder 436.
  • the encoder 436 imprints this information onto the terminator carrier signal in the form of a digital or analog code.
  • the encoded terminator carrier signal is then transmitted in synchronization with the base unit 14 by means of the oscillator 440 and carrier signal driver 438 to the base unit 14 via the terminator pickup lines 42, 44 and the conductors 22, 24 of the paired line 18.
  • the encoded terminator carrier signal is similar to the base carrier signal insofar as it has a frequency range greater than about 5 kHz, and preferably between about 5 kHz and about 100 kHz.
  • the terminator carrier signal most preferably has a frequency value of about 10 kHz when time multiplexed with the base carrier signal or about 15 kHz when frequency multiplexed with the base carrier signal.
  • the encoded terminator carrier signal typically has a voltage below about 15 volts within the prescribed frequency range and preferably has a voltage of about 0.5 volts.
  • the carrier signal When the encoded terminator carrier signal reaches the base unit 14 via the conductors 22, 24 common mode on the conductors with respect to ground, the carrier signal is received by the base pickup lines 34, 36 and carried to the low impedance input termination 218.
  • the first and second balanced capacitors 228, 232 act as low impedances to the terminator carrier signal, carrying the signal to the base circuit common 224.
  • the common mode terminator carrier signal is received by receiving the carrier voltage present on the ground 40 through the capacitor 274 into the carrier signal receiver 276 which is referenced to the base circuit common 224.
  • the carrier signal receiver 276 feeds the encoded terminator carrier signal to the limiter 278 where the amplitude of the terminator carrier signal is limited thereby and then to the decoder 280 where the encoded information on the terminator carrier signal is read.
  • the decoded information which comprises the values of the voltage magnitude for the induced signal measured at the terminator unit 16, is sent from the decoder 280 to the microcontroller 216 for processing.
  • the microcontroller 216 directs the reencoding of this information onto the base carrier signal so that the locator unit 12 receives encoded values of the voltage magnitude measured at both the base unit 14 and terminator unit 16 with receipt of the base carrier signal.
  • the voltage magnitude measured at the base unit 14 is always greater or equal to that measured at the terminator unit 16.
  • the locator unit is past the fault 20, such that the locator point 32 is between the terminator point 28 and the fault 20, no voltage magnitude is detectable at the base unit 14 while a voltage magnitude is measured at the terminator unit 16. Accordingly, if the operator observes a drop in the base carrier signal at the locator unit 12, the terminator carrier signal is checked. If the terminator carrier signal is greater than the base carrier signal, the drop in the base unit signal at the locator unit 12 is confirmed to be caused by location of the fault 20.
  • the drop in the base carrier signal is attributable to causes other than location of the fault, such as a change in depth, size, gauge, or paired line location of a buried paired cable.
  • FIG. 1 An alternative embodiment of a fault locating device and method of operation to that disclosed above is also provided.
  • the alternative embodiment is substantially the same as the fault locating device 10 of Figures 1-4 except for omission of the terminator unit 16 and its corresponding function of confirming the cause of a signal drop at the base unit 14.
  • Construction and operation of a fault locating device 10 absent a terminator unit 16 is readily apparent to the skilled artisan with reference to the disclosure provided herein.
  • inclusion or omission of the terminator unit 16 from the fault locating device 10 is entirely optional.
  • inclusion of the terminator unit 16 with the fault locating device 10 is preferred for buried paired cable applications to differentiate depth changes from faults and to provide a stronger carrier signal at a distance form the paired cable.
  • the terminator unit 16 is typically omitted from the fault locating device 10 for accessible paired cable applications.
  • a cable shield break is located in a cable having at least one conductor surrounded by a shield.
  • This alternate method of operation employs a combination of magnetic and capacitive carrier signal pickups.
  • Magnetic carrier signal pickup is initially used to identify a segment of the cable containing the shield break.
  • a segment of cable is defined for purposes of the present method as a length of cable having a ground point at each end.
  • the shield break is precisely located within the identified segment by means of capacitive pickup. Capacitive and magnetic carrier signal pickup require proper grounding of the cable segment at both ends thereof.
  • Proper grounding includes positioning a base unit at the base point of the segment to ground the conductor of the cable segment to the cable shield thereat. Proper grounding further includes either placing a terminator unit at the terminator point of the segment to ground the conductor of the cable segment to the cable shield or, alternatively, by physically grounding the conductor of the cable segment to the cable shield at the terminator point in the absence of a terminator unit.
  • the present method of locating a shield break in a segment of a cable 106 is described in greater detail hereafter.
  • the cable 106 has a shield 108 and at least one continuous concentric wire 110 enclosed thereby as a conductor, it being understood that additional continuous wires may also be present within the shield 108 to provide multiple conductors.
  • the method is performed by initially positioning the switch 76 in the locator unit 12 to connect the carrier signal processing circuit 60 with the carrier signal receiver 78 as shown in Figure 2.
  • the conductor 110 is grounded to the cable shield 108 at both ends of the segment and a base carrier signal is sent by the base unit along the conductor 110 of the cable 106 with reference to the cable shield 108 so that the base carrier signal on the conductor 110 is grounded to the shield 108.
  • the base carrier signal is generated and transmitted in a manner similar to that described above with respect to Figure 3, although no synchronization information nor information with respect to the characteristics of an induced signal need be encoded on the base carrier signal.
  • the base carrier signal is received magnetically by the coil 54 of the locator unit 12 and a base carrier signal indicator, such as voltage on the shield 108, is monitored as the locator unit 12 is moved along the length of the cable 106.
  • the base carrier signal voltage monitored at the locator unit 12 is at a maximum value when the locator unit 12 is adjacent to a segment of the cable 106 containing the shield break.
  • the switch 76 is repositioned to connect the capacitive ground reference circuit 98 with the carrier signal receiver 78 as shown in Figure 6.
  • the probe 52 is placed in contact with the cable 106, capacitively coupling the coil 54 to the shield 108.
  • This configuration enables the coil 54 to function as a capacitor, receiving the base carrier signal directly off of the shield 108 capacitively as the locator unit 12 is moved along the length of the identified segment of the cable 106.
  • the coil 54 sends the base carrier signal from the shield 108 to the locator circuit common 104 where the base carrier signal appears between the locator circuit common 104 and the capacitive ground reference 100.
  • the base carrier signal is amplified by the capacitive signal preamplifier 102 and sent to the magnitude preamplifier 88 for evaluation in the same as manner described above with respect to resistance fault location, thereby enabling precise location of the shield break within the identified segment of the cable 106.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Locating Faults (AREA)
EP96306285A 1995-09-01 1996-08-30 Localisation de défauts de lignes Withdrawn EP0762136A3 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106950464A (zh) * 2017-03-19 2017-07-14 沈阳顺义科技有限公司 一种基于路径优化的某型装甲车电缆故障检测系统

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0010841A1 (fr) * 1978-08-30 1980-05-14 BICC Public Limited Company Dispositif et procédé de localisation des défauts dans la gaine de câbles électriques souterrains
FR2451587A1 (fr) * 1979-03-16 1980-10-10 Minnesota Mining & Mfg Procede et systeme de controle pour localiser une anomalie sur un cable a conducteurs multiples

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0010841A1 (fr) * 1978-08-30 1980-05-14 BICC Public Limited Company Dispositif et procédé de localisation des défauts dans la gaine de câbles électriques souterrains
FR2451587A1 (fr) * 1979-03-16 1980-10-10 Minnesota Mining & Mfg Procede et systeme de controle pour localiser une anomalie sur un cable a conducteurs multiples

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106950464A (zh) * 2017-03-19 2017-07-14 沈阳顺义科技有限公司 一种基于路径优化的某型装甲车电缆故障检测系统
CN106950464B (zh) * 2017-03-19 2023-05-09 沈阳顺义科技有限公司 一种基于路径优化的装甲车电缆故障检测系统

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CA2183715A1 (fr) 1997-03-02

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